The present invention relates to a wire bonding apparatus for connecting a chip electrode of a semiconductor chip and an inner lead of a lead frame through a bonding wire.
A conventional wire bonding apparatus comprises an X-Y table having a bonding head, and an ultrasonic horn attached rotatably to the X-Y table. The ultrasonic horn extends in the Y direction, and a capillary which holds the bonding wire is secured to the end of the ultrasonic horn.
Operation of the conventional apparatus is as follows.
First, wire bonding between the chip electrode of the semiconductor chip and the bonding wire is performed. Then the capillary is raised slightly, and then the capillary is horizontally moved (reversed) to the semiconductor chip by a predetermined reverse amount. After that, the capillary is raised further until the total height is Z stroke, and then the capillary is lowered while being horizontally moved toward the inner lead.
When the capillary is raised, the capillary is not raised precisely in a vertical direction, because the capillary is operated by rotation of the ultrasonic horn. Raising the capillary therefore causes an error .DELTA.y in the Y direction.
However, when the error .DELTA.y becomes large with the enlargement of the loop length of the bonding wire, the error .DELTA.y causes problems that an inadequate loop bend or loop slack occurs on either the Y plus loop or the Y minus loop.